I did set the tabMinWidth first, but the result was… lackluster… to say the least (I like having ~50-100 tabs per window…). However, I JUST found out about userChrome.css before you wrote, and also found code that worked for it!

For anyone else interested:

Guide on creating the userChrome.css file: https://www.userchrome.org/how-create-userchrome-css.html

Code that should be added to the file: .tabbrowser-tab { min-width: 1em !important; clip-width: 1em !important; }